A wide variety of bleaching agents have been suggested for use in laundry and other cleaning compositions. For example, hypochlorite solutions may be used for such purposes, as can various peroxides and peroxide-generating bleaches and bleach activators. Materials such as sodium perborate, sodium percarbonate and the like have become commonplace for use in laundry detergents and other cleaning products.
One class of bleaching agents which are conventionally used under circumstances where laundered fabrics are subjected to concentrated light sources, such as direct sunlight as in a line drying operation, are the photobleaches. These valuable bleaches are relatively mild and safe to fabrics and dyestuffs, yet are quite effective in providing white, bright fabrics. In principle, the action of the photobleach involves the capture of energy from the sunlight and its conversion into a bleaching species on the fabric surface. A variety of such materials, especially those of the zinc phthalocyanine class, have been used commercially in laundry detergents for many years.
One problem associated with the use of any bleach is the ability to remove the impression of "dinginess" on fabrics which have aged. While the source of such dinginess is not known with particularity, it is believed that body soils, vagrant dyesuffs, tenacious soils and the like, eventually build up on fabric surfaces, with the result that the fabrics no longer appear new and white. Accordingly, there is a continuing search by detergent formulators for means to improve bleaching efficacy. For example, bleaches such as sodium perborate and sodium percarbonate have been improved by the use of the so-called bleach activator materials, including molecules such as tetraacetylethylenediamine (TAED), nonanoyloxybenzenesulfonate (NOBS), and the like.
However, with photobleaches very little improvement in performance has been seen, to date. The sulfonated zinc phthalocyanines currently in commercial use are, in general, accepted as providing maximum photobleach performance. Accordingly, the formulator of compositions comprising photobleaches has heretofore been constrained to seek other means for securing improved bleaching and cleaning benefits.
It has now been determined that certain chelating agents will interact with photobleaches to increase their absorbency in the visible light spectrum. While not intending to be limited by theory, it may be speculated that photobleaches in the presence of a chelant appear to form a more active bleach species in solution that can absorb on the fabric surface. During the drying process, this species of "photobleach-chelant" can absorb more energy which is used to activate oxygen to an activated state which will oxidize soils, especially those containing double bonds in their molecular structure. Alternatively, the photobleach-chelant may require less energy per molecule to absorb than does photobleach, alone, to be energized and activate the oxygen species responsible for the bleaching. Whatever the reason, this increased absorbency means that the photobleach will more efficiently and effectively produce the desired bleaching species. Accordingly, it has now surprisingly been determined that photobleaches used in combination with chelants in the manner of the present invention provide improved whiteness maintenance performance.
It is an object of the present invention to provide improved photobleaching, especially of laundered fabrics. It is another object herein to provide improved photobleaching and laundering compositions. These and other objects are secured herein, as will be seen from the following disclosures.